/*
 * Copyright (C) 2022-2025 Huawei Technologies Co., Ltd. All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

package io.sermant.xds.service.traffic.management.handler;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.ServiceLoader;

/**
 * ChainBuilder, String all spi loaded handlers in order of priority
 *
 * @author zhouss
 * @since 2022-07-05
 */
public enum HandlerChainBuilder {
    /**
     * singleton
     */
    INSTANCE;

    private static final int HANDLER_SIZE = 4;

    private static final List<AbstractXdsChainHandler> XDS_HANDLERS = new ArrayList<>(HANDLER_SIZE);

    static {
        ClassLoader classLoader = HandlerChainBuilder.class.getClassLoader();
        for (AbstractXdsChainHandler handler : ServiceLoader.load(AbstractXdsChainHandler.class, classLoader)) {
            XDS_HANDLERS.add(handler);
        }
    }

    /**
     * build Xds chain
     *
     * @return ProcessorChain execution chain
     */
    public XdsHandlerChain buildXdsHandlerChain() {
        Collections.sort(XDS_HANDLERS);
        final XdsHandlerChain xdsHandlerChain = new XdsHandlerChain();
        XDS_HANDLERS.forEach(xdsHandlerChain::addLastHandler);
        return xdsHandlerChain;
    }
}
